1. Field of the Invention
The present invention relates to the DNA coding for phosphoserine phosphatase of coryneform bacteria. The DNA may be utilized for microbiologic industry, such as breeding L-serine producing coryneform bacteria.
2. Description of the Related Art
As a conventional method of producing L-serine by fermentation, there has been reported the method in which a bacterial strain capable of converting glycine and sugar into L-serine is used in a medium containing 30 g/L of glycine to produce at most 14 g/L of L-serine. The conversion yield amounted to 46% (Kubota, K., Agricultural Biological Chemistry, 49, 7–12 (1985)). Using a bacterial strain capable of converting glycine and methanol into L-serine, 53 g/L of L-serine can be produced from 100 g/L of glycine (T. Yoshida et al., Journal of Fermentation and Bioengineering, Vol. 79, No. 2, 181–183, 1995). In the method using Nocardia, it has been known that the L-serine productivity of the bacterium can be improved by breeding those strains resistant to serine hydroxamate, azaserine or the like (Japanese Patent Publication No. 57-1235). However, these methods involve use of glycine that is a precursor of L-serine and include complicated operation and is disadvantageous from the viewpoint of costs.
As strains that can ferment L-serine directly from a sugar and do not need addition of the precursor of L-serine to the medium, there has been known Corynebacterium glutamicum that is resistant to D-serine, á-methylserine, o-methylserine, isoserine, serine hydroxamate, and 3-chloroalanine but the accumulation of L-serine is as low as 0.8 g/L (Nogei Kagakukaishi, Vol. 48, No. 3, p. 201–208, 1974). Accordingly, further strain improvements are needed for direct fermentation of L-serine on an industrial scale.
On the other hand, regarding coryneform bacteria, there have been disclosed a vector plasmid that is capable of autonomous replication in the cell and having a drug resistance marker gene (cf. U.S. Pat. No. 4,514,502) and a method of introducing a gene into the cell (Japanese Patent Application Laid-open No. 2-207791). These techniques have been utilized for breeding L-amino acid producing bacteria. As for L-serine, it has been found that L-serine productivity of coryneform bacteria having the L-serine producing ability is improved by introduction of a gene coding for D-3-phosphoglyceratehydrogenase whose feedback inhibition by L-serine is desensitized (serA gene)(European Patent Application Laid-Open No. 943687), or amplification of a gene coding for phosphoserine phosphatase (serB) or phosphoserine transaminase (serC) (European Patent Application Laid-Open No. 931833). There has been known serB gene in Escherichia coli (GenBank accession X03046, M30784), Yeast. (GenBank accession U36473), Helicobacter pylori (GenBank accession AF006039), however, serB gene of coryneform bacteria has not been known.